Piezoelectric materials can perform two desirable functions. When subjected to mechanical stress, e.g., bent, compressed or flexed, piezoelectric materials can generate an electric charge which can then be stored or used. Further, if an electric field is applied to a piezoelectric material, it can cause the piezoelectric material to deform.
A manufacturing process has been developed for making piezoelectric ceramic materials into flexible fibers. More specifically, Advanced Cerametrics Inc. (ACI) has created a flexible lead zirconate titanate (PZT) ceramic fiber capable of harvesting energy, actively controlling structures or powering electronic systems.
Piezoelectric fibers may be used in a “smart” sensor to sense the health of a structure or perform self-adjusting or vibration damping functions. In this regard, piezoelectric materials, such as ACI's PZT ceramic fibers, can be embedded into a composite material or attached to a structure's outside surface. Such an assembly takes advantage of the fiber's mechanical properties by first sensing a change a motion. This produces an electrical signal that can be sent to an electronic circuit. The electronic circuit can then relay a signal that either stiffens or relaxes the fibers, producing a self-adjusting or “smart” structure. For example, “smart” tennis rackets have been developed that use ACI's PZT fibers to actively damp vibrations. Transducers including piezoelectric fibers are provided on the racket frame to generate low-current electricity that is transmitted to an electronic circuit disposed in the racket's handle. The stored electric energy is released to flow back to the fibers which deform to counteract the vibration.
As is widely known, the largest part of the high stresses that tend to shorten the life span of a wind turbine will occur at high wind velocities. Wind turbines are conventionally equipped with measurement systems and control systems to enable them to independently react to changes in wind conditions. These systems are designed to maximize energy capture while minimizing the impact of fatigue and extreme loads. The effectiveness of these control systems is constrained by limitations on sensor technologies and the mechanical systems that control the pitch angle of the blades, the rotation of the rotor, and the like. In this regard, measurement systems and detectors local to the particular wind turbine necessarily operate in a reaction mode, reacting to conditions already existing at the wind turbine. The known approach of monitoring wind conditions and reducing the power output in case of high wind velocities makes it possible, for example, in a variable-speed pitch plant with a control algorithm for controlling the rotor speed and/or pitch angle to obtain high ratios between the rotor diameter and the generator performance without an accompanying increase in component fatigue.